Mobile devices such as cellular phones, personal data assistant devices, portable computers, etc. are becoming ubiquitous recently. These mobile devices are used to communicate with other mobile devices, personal computers, and servers through a wireless network. Particularly, mobile devices are being used to talk; receive and send text messages and emails; make reservations to hotels, rental cars, or tickets; create and record appointments; play video games; or watch TV or movies. The adoption of these mobile devices in everyday life gives great convenience to users.
Recently, mobile devices are increasingly being used to participate in audio or video conference calls.